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A new design methodology recently introduced for looped networks is now applied to branched networks. The methodology is based on cost analysis minimisation, network mathematical simulation under normal and failure states and reliability estimates. It is capable of obtaining not only an adequate value for the global reliability of a network but also the appropiate total design demand. This paper then presents a deeper insight into the comparison between looped and branched networks by applying the methodology to both types of networks and comparing the results in terms of cost and reliability. Considerations regarding available reliability definitions are also included which seem to favor volume-type definitions in practice. Results provide a rational foundation to reveal the superiority of looped networks over comparable branched networks by applying quantitative cost evaluations.

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Optimization of water supply looped networks has attracted a great deal of attention from researchers for more than 30 years. As the classical water supply looped network optimization problem is mathematically non-convex and multimodal, the resulting solution of most approaches is uncertain in the sense of how close it is to the ''best'' solution. In many cases, this ''best''' or ''global'' solution is invoked and pursued only intuitively without a clear understanding of its meaning. This paper discusses what is involved in ''global'' solutions and the role that pipe flow distribution can play to deal with non-convexity and multimodality in a new context. The author has introduced this new context recently after formulating a new objective function capable of finding a looped network that can be economically more attractive than its related branched one. Therefore, the convenience of an approach dealing with flows and heads, as relevant decision variables, is encouraged in this paper and its advantages enumerated under the new concepts.The entropy approach is studied critically and an example is provided for comparison with the proposed approach.